1. Field of the Invention
The present invention relates to an oceanic structure for ocean development such as a platform for sea bed oil excavation, a one-point mooring buoy type mooring facility for transfer of crude oil to and from large tankers, a deep sea anchor and a measurement table and more particularly a gravity type oceanic structure and its stable installation.
2. Description of the Related Art
As a fixing technology of a bottom settling type oceanic structure, two methods are known. One is a gravity type fixing with which the structure is fixed by its own weight in water and the other is a piling type fixing with which piles are driven into the foundation and the structure is fixed to these piles.
However, in gravity fixing, since the structure's buoyancy is proportional to its volume in water, the weight of the structure itself must be great in order to settle itself on the sea bed and fix itself. Especially, in order to fix the structure against horizontal forces such as earthquake force and ice pressure, the bottom surface of the structure must adhere to the sea bed surface tightly to increase the pressure (effective contact pressure) which is transmitted from the bottom surface of the structure to the sea bed foundation surface, and the strength of the sea bed foundation must be fully utilized. Therefore, the weight of the structure itself must be even larger and high cost is unavoidable.
In the pile structure, the water depth in which this structure can be applied is limited, and when the structure is removed, the piles must be removed too as they are regarded as parts of the structure; and hence high cost is again unavoidable.